1. Field of the Invention
This invention relates to power supply regulation and particularly to establishment and regulation of both a low voltage dc supply and the establishment and regulation of a high voltage dc supply for operating complex high intensity, gaseous discharge lamp circuits.
2. Description of the Prior Art
The maintenance of power to a load, even in the presence of momentary interruptions, is critical in many applications. However, none may be more critical than in systems wherein the load is represented by high intensity, gaseous discharge lamps. The reason for this is that even momentary cessation of power will cause the lamps to go out, requiring normally two minutes and longer to restrike and even longer to reach full brightness.
In addition to the maintenance of power in the presence of line voltage interruptions, it is also highly desirable to maintain a relatively stable voltage to many loads, such as lamp circuits, even if there are no line voltage interruptions. The main reason for this is to ensure against fluctuations that may shorten lamp life or otherwise cause lamp injury.
Circuits in the past have employed combinations of resistors, capacitors and even diodes to provide regulation to power supplies, but these have amounted to little more than filtering systems preventing widely varying excursions.
Circuits providing power regulation to the power section of circuits connected to operate high intensity gaseous discharge lamp networks have previously been developed. One circuit somewhat suitable for providing a degree of desirable regulation is disclosed in FIG. 7 of copending Patent Application Ser. No. 898,309, filed Apr. 20, 1978, a continuation of Patent Application Ser. No. 654,926, now abandoned, commonly assigned. In that circuit, a phototransistor controlled across the dc output of the power supply determines the application of gate voltage to a triac. This conduction timing determines the operation of a bridge in the power supply, and hence provides regulation.
This circuit does not ensure against sudden surges opening the power circuit. More importantly, perhaps, it does not ensure the maintenance of a dc voltage output in the presence of momentary interruptions of the line source of ac power.
Another circuit for overcoming some of the quick response problems of this earlier circuit is disclosed in copending Patent Application Ser. No. 808,969, filed June 22, 1977, also commonly assigned. In that circuit, there was the fundamental problem of not quickly removing regulation in the presence of ac source voltage outages and therefore, the regulation circuit attempted regulation at the very time that regulation was not possible. This circuit assures that under these conditions, the circuit operation will be dependent on dc voltage stored on large storage capacitors. Further refinements of this latter circuit to overcome some of the difficulties still remaining are disclosed in Patent Application Ser. No. 927,554, filed July 24, 1978, also commonly assigned.
The advent of sophisticated dimming and other control circuits have made it desirable to supply not only closely regulated high power dc voltage to high intensity, gaseous discharge networks, but also to apply closely or highly regulated low power dc voltage to such networks for providing power to these control circuits, a problem not addressed in the prior art circuits discussed above.
It is highly desirable, of course, to derive power for operating both high voltage circuit components, as well as low voltage components, from a common high voltage ac source. As mentioned above, it is also then desirable that both types of voltages be regulated. It is further important that high voltage not be supplied to the lamp network if there is an absence of the low voltage output. In addition, it is important that the most suitable type of regulation circuit be provided for the production of high voltage regulation as well as low voltage regulation, which do not employ the same kind of regulation techniques. For example, switching regulation at low power is highly desirable since it is relatively simpler than phase-controlled bridge operation, more efficient and creates less heat. Furthermore, switching regulation at relatively high frequency, e.g., 20 KHz, allows the use of relatively small components, which are correspondingly less expensive. Fast switching still accomplishes suitable fast reaction for changes in line supply voltage or changes in load. On the other hand, phase-controlled bridge operation for high power is desirable since large and expensive switching semiconductors do not have to be employed that would otherwise be needed to handle large voltages and currents.
Therefore, it is a feature of this invention to provide an improved dc regulation circuit having the dual functions of providing both high voltage dc and low voltage dc for such applications as to one or more high intensity, gaseous discharge lamp systems, the absence of low voltage dc inhibiting development of high voltage dc.
It is another feature of the present invention to provide an improved high voltage dc power and control network providing phase control to a bridge regulator as developed from precision timer networks, the outputs of which are suitably isolated from the gate drive elements providing the phase control.
It is still another feature of the present invention to provide an improved low voltage switching regulator employing a pulse width modulator for providing constant frequency, variable duty cycle switching to the output power device thereof.